This invention relates to a process and apparatus for increasing the size of ammonium sulfate crystals, e.g., from an average size of about 0.5 mm to an average size of at least about 1.0 mm. More importantly, this invention relates to the preparation of ammonium sulfate crystals of uniform size as well as uniform moisture.
The manufacture of ammonium sulfate is an important industrial process and is the subject of a considerable body of patent and non-patent literature. See, e.g., U.S. Pat. Nos. 1,266,212; 1,919,707; 2,043,067; 2,092,073; 2,099,079; 2,102,107; 2,178,082; 2,226,101; 2,228,742; 2,368,901; 2,423,794; 2,424,207; 2,599,067; 2,631,084; 2,659,659; 2,782,097; 2,795,487; 2,805,125; 2,874,028; and 2,895,800, and Parkash, "Residence Times of Crystals in a Fluidised Bed Crystallizer", Chemistry and Industry, pp. 919-920, Jun. 3, 1967; Parkash et al., "Crystal Growth in Fluidized Beds", Indian Chemical Engineer, pp. 3-6, January 1968; Vragov, "Investigation of Ammonium Sulfate Crystallization in a Pseudo Liquified Layer", Sb. Nauch. Tr., Kuzbas. Politekh. Int., No 26, 1970; and, Postnikov et al., "Crystallization of Ammonium Sulfate in a Two-Circuit Device With a Circulating Suspension", Koksii Khimiya, No. 4, pp 24-27, 1983.
It has long been recognized that the tendency of ammonium sulfate crystals to cake on standing is lessened with increased size of the crystals. It has therefore been a goal of many of these manufacturing processes to provide ammonium sulfate crystals of larger size, e.g., averaging at least about 1.0 mm. Typically, such increased crystal size has been achieved through control of the crystallization process.
Even more significantly, where crystal size is relatively uniform, the tendency of ammonium sulfate to cake on storage is reduced. The reduced tendency to cake is further emphasized when the particles have a uniform moisture distribution. As used herein, "uniform particle size" means that the particles deviate no more than about +10% from the average particle size. For example, where the average particle is 1 mm, the smallest will be 0.9 mm and the largest 1.1 mm.